Re: [PATCH 0/3] ALSA: pcm: add tracepoints for PCM params refinement

[Takashi Iwai <tiwai@suse.de>]

On Wed, 07 Jun 2017 01:46:42 +0200,
Takashi Sakamoto wrote:
> 
> Hi,
> 
> This patchset is a part of my previous RFC and go for upstream.
> [alsa-devel] [PATCH RFC 00/21] ALSA: pcm: add tracepoints for PCM params operation
> http://mailman.alsa-project.org/pipermail/alsa-devel/2017-May/120548.html
> 
> In ALSA PCM interface, applications can get hardware capability by ioctl(2)
> with SNDRV_PCM_IOCTL_HW_REFINE/SNDRV_PCM_IOCT_HW_PARAMS in a shape of
> 'struct snd_pcm_hw_params'. In kernel side, relevant processing is somewhat
> complicated and developers sometimes have hard time to debug drivers for PCM
> constraints and rules. This patchset adds tracepoints to assist their work.
> 
> Changes:
>  - change print format
>  - rename events
>  - refactoring in the RFC will be done in my later work.
> 
> 
> This patchset adds two events; 'hw_interval_param' and 'hw_mask_param' in
> 'snd_pcm' subsystem. When these events are probed, tracer outputs below
> lines:
> 
> hw_interval_param: 0,0,0,0 000/023 BUFFER_SIZE 0 0 [0 4294967295] 0 1 [0 4294967295]
> hw_interval_param: 0,0,0,0 000/023 BUFFER_BYTES 0 0 [0 4294967295] 0 1 [128 65536]
> hw_interval_param: 0,0,0,0 000/023 TICK_TIME 0 0 [0 4294967295] 0 0 [0 4294967295]
> hw_mask_param:     0,0,0,0 001/023 FORMAT 00000000000000000000001000000044 00000000000000000000001000000044
> hw_interval_param: 0,0,0,0 002/023 SAMPLE_BITS 0 1 [0 4294967295] 0 1 [16 32]
> hw_interval_param: 0,0,0,0 003/023 SAMPLE_BITS 0 1 [16 32] 0 1 [16 32]
> 
> The first field represents PCM character device and subdevice for probed
> runtime of PCM substream. In the above case, '/dev/snd/pcmC0D0p' and
> first subdevice are used for runtime of PCM substream.

How about using snd_pcm_debug_name()?  It'll be like "pcmC0D1c:2" and
slightly more understandable than "0,1,1,2".


> The second field represents id of each rule applied to the runtime, and
> the total number of rules added to the runtime. Basically, when the rule
> is applied to the runtime, these events are probed, but lines with id 0
> are exceptions. They're application of constraints to the runtime.
> 
> The third field is name of parameter in the runtime. The rest fields
> depends on type of the parameter (mask/interval).
> 
> 
> In ALSA PCM core, runtimes get 22 (or 21) rules as a default. In a below
> sample, the 21st rule is added by driver (snd-soc-imx-ssi.ko). The rest is
> added by snd-pcm.ko. In detail, please see 'snd_pcm_hw_constraints_init()'
> and 'snd_pcm_hw_constraints_complete()' in 'sound/core/pcm_native.c'.
> 
> hw_interval_param: 0,0,0,0 019/023 PERIOD_TIME 0 0 [0 4294967295] 0 0 (166 4095875]
> hw_interval_param: 0,0,0,0 020/023 BUFFER_TIME 0 0 [0 4294967295] 0 0 (333 4096000]
> hw_interval_param: 0,0,0,0 021/023 PERIOD_SIZE 0 1 [16 32767] 0 1 [16 32766]
> hw_interval_param: 0,0,0,0 022/023 BUFFER_BYTES 0 1 [128 65536] 0 1 [128 65536]
> hw_interval_param: 0,0,0,0 023/023 RATE 0 0 [8000 96000] 0 0 [8000 96000]
> hw_mask_param:     0,0,0,0 001/023 FORMAT 00000000000000000000001000000044 00000000000000000000001000000044

Could you add these explanations in Documentation?  The cover letter
is gone at merging.


thanks,

Takashi